"...the universe appears to be expanding at an accelerating

[lukman]

We have known from scientist that our universe is expanding space in accelerating speed. <br /><br />Now, The most remote object observe is 13bly away. The actual distance of the object is now 75bly. So, in 13billion years, the object is now 62bly away, that is extremely fast speed. <br /><br />I am not questioning how it can be. My question is, what is the current acceleration of the universe that is better than doing 62bly in 13billions years. <font color="blue"> "...the universe appears to be expanding at an accelerating rate" </font>/safety_wrapper> <div class="Discussion_UserSignature"> </div>

 

[weeman]

I'm having a bit of a hard time following what you're saying.<br /><br />When we see the farthest objects at 13-14bly, they show very immense red-shifts, almost indicating that they are traveling faster than light. Of course the galaxies couldn't possibly going faster than light, only the dimensions of space around them. But lets say that they are traveling at the speed of light. If the light left them 13 billion years ago, they might be around 26bly from Earth today. This would give us an estimated 56bly diameter for the known observable universe. <br /><br />Also, many people might speculate that when light left an object 13bly away, it actually took longer than 13 billion years to reach Earth, because it is traveling against the expansion. <br /><br />However, this idea is a large misconception. Through space, light travels at the same speed, and reaches a destination at the same time whether it's in an expanding universe or not. Even if the red-shifts of the most distant galaxies make them appear to be moving faster than light, it is only the dimensions of Space, not the galaxies themselves.<br /><br />So, I'm not sure if anyone can really say what the current acceleration of the universe really is. If we see the expansion starting to pick up speed several billion years ago, won't we have to wait another several billion years to see the acceleration as it is today? <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>

 

[lukman]

<blockquote><font class="small">In reply to:</font><hr /><p> I'm having a bit of a hard time following what you're saying. <p><hr /></p></p></blockquote><br /><br />Sorry, perhaps my poor english (not my native language) and my understanding of the universe. Anyway, you get my point. Basically, i agree and know what you mean, but way too hard for me to understand because i am not from science background, only pure interest in science and astronomy. <img src="/images/icons/laugh.gif" /><br /> <div class="Discussion_UserSignature"> </div>

 

[enigma10]

I think the best basic example i have seen concerning the speed of light is the baseball and car analogy. Think it was even Dragon04 that made the analogy. Not sure.<br /><br /> Anyway. It concerns the speed of light represented by the baseball being thrown from the car in various directions. Now you have to discount wind in the analogy, and realize it is not exact in its comparison to the real thing, but its conceptually accurate.<br /><br /> What you'll find is no matter what speed the car is going, when you throw the ball, it will only travel at set speed. This , of course, can be painfully realized if you've ever gone 60-70 and tried to to throw a ball forward. Once the ball leaves your hand, it travels at whatever force/speed applied, and no more.<br /><br /> <div class="Discussion_UserSignature"> <em>"<font color="#333399">An organism at war with itself is a doomed organism." - Carl Sagan</font></em> </div>

 

[alokmohan]

The question is if Universe is accelarating?

 

[lukman]

If universe expand like ballon, and there is no way in 3D for us to see the center and no way to tell where is the farthest point. So for me, i dont really sure if the age of the universe is something close to the farthest object observed. <div class="Discussion_UserSignature"> </div>

 

[weeman]

In a sense we are looking to the edge of the observable universe because we are looking back to its beginning. However, many people might not classify this as the edge of the universe, most people would visualize an actual end to the material universe. <br /><br />As for the comoving universe, I understand the concept that light has to travel further because of the expansion. In my post up above this one, however, I said that the expansion affects the speed of light in no way.<br /><br />I mentioned the idea of a co-moving universe to my astronomy teacher last semester, and he made it sound like he didn't really agree with the idea of a co-moving distance. He had said exactly what I said in my previous post, he believes that if light left an object 13bly away, it should now be about 26bly away. <br /><br />I guess I sort of believe in both ideas, probably because I can't fully understand both quite yet <img src="/images/icons/smile.gif" /> <br /> <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>

 

[SpeedFreek]

<font color="yellow"> I mentioned the idea of a co-moving universe to my astronomy teacher last semester, and he made it sound like he didn't really agree with the idea of a co-moving distance. </font><br /><br />All the co-moving distance means is the distance objects are from us <i> now </i> as opposed to the distance they were from this point in space when the light left them.<br /><br />It seems to me that if he doesn't agree with the idea of a co-moving distance, he doesn't agree with the idea that the universe is expanding. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[weeman]

I guess I sort of worded it in an odd way. <br /><br />He believes that the universe is expanding, but doesn't believe that objects might be further away than really we think, due to the expanding universe. For example, some people say that a galaxy that appears to be 13bly away when its light reaches us, might actually be more than just double that distance now. It could very well be 60bly, 70bly, or even 100bly away, because it took a long time for light to reach us since it is traveling against the expansion. This is where my professor looked at things differently. He believes that the expansion affects the lights travel in no way, it is always traveling at its own speed. So, he is basically saying that it wouldn't take light 20bly to reach Earth when it left an object that was only 13bly away. It took 13 billion years for the light to reach Earth from a galaxy that is 13bly away, despite what the expansion rate is. It didn't take 16 billion years, or 24 billion years, or 30 billion years, and so on.... <br /><br />I hope you can follow what I am saying, it's kind of hard to describe <img src="/images/icons/tongue.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>

 

[lukman]

Doesn't make sense, do you mean that whatever we see in the sky was not the past? because that is what sounded too me. If it was past, then you need to add expansion rate to it to determine current position. <div class="Discussion_UserSignature"> </div>

 

[weeman]

It still is the past, it still took the light however much time to reach Earth. I don't fully understand it either, and I don't entirely believe in it, I debated with him a lot on this subject on the class message forum <img src="/images/icons/smile.gif" /> I am just trying to give different perspectives on this subject. <br /><br />Although I'm not sure where you're getting confused when you say it wouldn't be in the past. If light leaves point A, and travels to point B, then B will see A's light as it existed in the past. This would be the case if the distance between them was increasing, or they where stationary. <br /><br />Am I understanding your question correctly? <img src="/images/icons/tongue.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>

 

[dragon04]

<font color="yellow">I think the best basic example i have seen concerning the speed of light is the baseball and car analogy. Think it was even Dragon04 that made the analogy. Not sure.</font><br /><br />Yes, that was my analogy. And admittedly, an over simplistic one.<br /><br />But it's clear that by some of the questions asked, the most simplistic frame of reference has to be provided to get the questioner "in the ballpark", so to speak.<br /><br />Now, we can move onto more advanced concepts. The fact that the author of this post brings up an issue that we can't neatly explain can be expanded on.<br /><br />Given the current theory on the rate of expansion of the Universe given the observable data we have puts us in a quandry.<br /><br />In order to explain how a Universe pretty much unilaterally agreed that is only maybe half as old (or less) as red shift observations tell us, we have a problem.<br /><br />Either my baseball analogy is incorrect (although its been experimentally and mathematically proven) or there are forces at work that we still don't understand and can't explain.<br /><br />In particular, there is more mass in the Universe that we are aware of to plug and play the data that our observations would support (dark matter) or there is a force as yet undescribed (dark energy) that can be plugged in to explain the dilemma posed. Or perhaps a combination of both.<br /><br />Let's go back to the "inflating balloon" notion. It would be a nice explanation provided that some "central force" is expanding the universe.<br /><br />As the Universe expands, the surface of the balloon would appear to have the effect of any individual point (galaxy) moving away from every other point at an accelerating rate simply due to the increasing surface area of the balloon.<br /><br />However, Relativity doesn't like that balloon very much. Relativity says that the balloon can only expand as fast as its equations allow for. And that is <b>not</b> what we are observing.<br /><br /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[lukman]

One more question. My opinion is: 13bly away object has nothing to do with the age of universe. Is that true? Consider the alternatives if universe expanding in different rate, or even if it was contracting now. <div class="Discussion_UserSignature"> </div>

 

[six_strings]

great thread <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[ianke]

Here is something I posted in another thread because I too have trouble with just looking at one option to explain the acceleration of expansion<br /><br />Note: It is just one of many options and is not my intent to push this theory. I only intend to say that there is other ways of looking at the data.<br /><br />"It appears to me that alternate explainations for the observed speed up could just as easily fit by changing our perception of the data, or by changing the size, speed,etc. of the universe in the original equations. I can conceive of many other options that would explain the observed without the invention of magic. I don't mean to say that Dark Energy is absolutely false. It may well be that we find it to be true. I just think that the theory gets way more weight than the data merits. <br /><br />To put this argument to the test, let me give an example of an hypothesis that could fit. For this purpose I will assume that the universe is not it's accepted size but many orders of magnitude bigger, and we are not at the center. Also, let us imagine that the universe is not still expanding, but rather it is already starting to contract. Third, the universe is only about 13 billion years in age. Last, let us assume that the original kinetic energy of everything, from the big bang on, was widely varied. (I can see where someone might see these as wrong, but this is just one hypothetical starting point) <br /><br />Given the above premises, one could expect to see exactly what is observed in our data. Here are some supporting argunents... <br /><br />1. We would not see any further in time or distanct than from a point that light started to exist. So we only see a small part of the cosmic whole. <br /><br />2. This is the part that may take some immagination. Those things that have a smaller original kinnetic energy at the start would start to fall back to the absolute galactic center before those masses with an original higher speed. Therfore an acceleration could be obser <div class="Discussion_UserSignature"> </div>

 

[SpeedFreek]

Yes I agree there could be many other ways of looking at the data. Our interpretation of what the universe is doing could be skewed or completely wrong.<br /><br />All we can do is try to amass as much data as we can, and then find ways to interpret it that fit with what we think we already know, and then recheck what we think we know and reinterpret the data until we find the answer or give up trying! <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[ianke]

Hi speedfreek,<br /><br />In your post...<br />"All we can do is try to amass as much data as we can, and then find ways to interpret it that fit with what we think we already know, and then recheck what we think we know and reinterpret the data until we find the answer or give up trying!"<br /><br />You can say that again.<br /><br /> We are limited in our ability to pin down very much about the extremes of the cosmos. How big, how fast, how much there is all seem to be questions that are (at best) left to what premise you allow yourself to accept as a starting place.<br /><br />With reguards to expansion:<br />1.If you assume that what mass we see amounts to about 4% of expected, and Dark Matter makes up 22%, leaving 74% to be a Dark Energy, then you really are saying that you know what the total value of the universe must be. To me, That is quite a statement. I have been looking at the threads both here and elsewhere. I have read every link given in the past 2 months on the subject of expansion, accelerating expansion, what shape and how big the universe is. In all of those links and discussions not one time has anyone given a good enough reason to pin the universe to a known size that adds up to the Dark Matter inthusiast's "100%" . <img src="/images/icons/tongue.gif" /><br /><br />2. There are those that will tell you about how an observation that has been done means the universe fits this or that. ("It must be that the universe is speeding up it's expected expansion because the red shift is too far. etc. etc.) They accept these postulates without being able to disprove other explainations of that same said data. Again we make a rather large assumption when we do this. A good "theory" should be able to prove that the alternate explainations are false. To date, at least as far as the red shift discrepancy, this has not been done to a point that reasonable arguments can be made for the speeding up of space time expansion. <img src="/images/icons/tongue.gif" /><br /><b></b> <div class="Discussion_UserSignature"> </div>